Gad Maor instead of the workaround that you're using, you could download and install a plugin build with the proposed change to add support for separate LFS credentials. Report your results on that pull request so that others know what you observed.
If that solves the problem then you've avoided the workaround and have helped the Jenkins community evaluate the pull request.
If that doesn't solve the problem, you return to your workaround and have helped the Jenkins community evaluate the pull request.
You'll need to install the git client plugin beta release from the experimental update center as well, which will also help the Jenkins community.